This disclosure relates generally to proximity detection systems at work sites, and in particular to personal alarm devices (PADs) for use with an interactive magnetic marker field and proximity detection system.
Mining is a very diverse industry, in many ways. The diversities include the differing products being mined, geologic formations from which the product is being extracted, locations throughout the world, strategies for mining, countless types of equipment used, mining above ground and underground, to mention a few examples. In most cases, equipment is being used to accomplish or to assist in the mining process, including mining machines and vehicles. Such vehicles and mobile equipment may be used for above and/or below ground operations. Examples of the equipment include: road construction equipment such as trucks, road graders, rollers and pavers; surface mining equipment, such as for use with gravel and sand operations, front end loaders, trucks, dozers, conveyors and other items; underground mining equipment such as continuous miners, shuttle cars, conveyors, crushers, load-haul-dump vehicles, man-trips, tractors, and other items. The equipment also includes fork lifts, cranes, and trucks used at warehouses and shipping ports.
Much too often, workers are injured while doing their jobs. As more equipment is used and as that equipment has become larger and more powerful, and as the operations have become more complex, many of the injuries and fatalities result from workers being struck or crushed by the mining machines or by collisions between vehicles.
Many methods have been devised to warn people against being struck, pinched, crushed or otherwise harmed by vehicles and mobile equipment. Unfortunately, the systems that have been devised to help protect people and property in these industrial operations, such as proximity detection and collision avoidance systems, have usually not been very effective. A new proximity detection system was developed and successfully demonstrated for use on continuous miners, as disclosed in U.S. Pat. No. 7,420,471 (the '471 patent), U.S. Pat. No. 8,169,335 (the '335 patent), U.S. Pat. No. 8,232,888 (the '888 patent) and U.S. Pat. No. 8,446,277 (the '277 patent), and US patent publications 2009/0322512 (the '512 publication) and 2012/0268261 (the '261 publication), which patents and publications are herein referred to collectively as the “Frederick patents,” the disclosures of which are incorporated herein by reference in their entireties.
An objective of the '471 patent is to help prevent the crushing or pinning of personnel who are remotely controlling a continuous miner, and to help protect other personnel assisting in use of the continuous miners. The '471 patent also envisions to provide protection to personnel from other types of mobile equipment and machines. The system of the '471 patent employs a magnetic marker field and an active architecture that incorporates two-way communication between the worker and the machine that the worker is near. Warnings are given to workers who are too close to the miner. Warnings are also provided to the operator of the machine. Provisions are made to immobilize the equipment until personnel are able to reach a safer position.
The magnetic fields used in the '471 patent system oscillate at low frequencies and can be effectively used to mark off warning zones, danger zones and silent zones. Although the maximum practical range of such low frequency magnetic fields may be as much as one hundred feet, in most applications that is more than is needed or desirable for most equipment. Typical very large off-highway haul trucks would probably be best served with a warning zone in the range of eighty feet and a danger zone in the range of thirty to forty feet. In some applications, such as remotely controlled continuous miners, it is necessary for the operator to remain within a range of five to ten feet of the miner much of the time in order to maintain good visual contact with the machine and the immediate surroundings. The zones are shaped to be longer in the direction of travel or movement, but shorter in directions perpendicular to the direction of travel. In underground mines, the low frequency magnetic fields pass unimpeded through earth formations so that a worker that is around a corner, not in line of sight, or otherwise obstructed, will still be visible to the marker field. These magnetic fields do not radiate from antennas but simply expand and contract around the element that produces them, and are well suited for marking boundaries between silent zones and warning zones.
The embodiments of the invention are particularly applicable to work sites that require personnel to be in close proximity to various hazardous elements, such as machines, mobile equipment, remotely controlled machines, and operated vehicles. Such work environments may include locations that are inherently dangerous and should be avoided or entered only with great caution. Examples of such work environments include surface mining, underground mining, sand and gravel operations, road construction, warehouses, shipping docks, coke plants, etc. Hundreds of people are killed each year in the U.S. in such work environments. Workers are sometimes struck, pinched, crushed or otherwise harmed while performing their jobs in such environments. Collisions between the various elements at the work sites need to be avoided also to avert property damage.
Referring now to FIG. 1, there is illustrated a simplified example of a work site in which a proximity detection system is implemented. FIG. 1 shows a truck 304 on which a magnetic field generator 81 is mounted. The magnetic field generator 81 generates a magnetic field 92 that surrounds the truck 304. The edge of the magnetic field 92 generated by the magnetic field generator 81 corresponds to the border of a Warning or Danger Zone surrounding the truck 304. A worker 301 within the boundary of the Warning or Danger Zone is in potential danger from being struck or otherwise injured by the truck 304. The worker 301 carries a personal alarm device 60. If the worker 301 and, correspondingly, the personal alarm device 60 are within the magnetic field 92 created by the magnetic field generator 81, the personal alarm device 60 detects the presence of the magnetic field 92 and issues a visual or audio warning. In embodiments of the magnetic field warning system, as detailed in the '888 patent, multiple magnetic field generators 81 may be used to generate Warning and Danger Zones having a complex shape around the truck 304 or other equipment or areas. These zones may be adjusted in both size and shape. In addition, safe zones may be designated near the truck 304 in which a personal alarm device 60, while within the magnetic field 92, does not generate a warning signal to the worker 301.
FIG. 2 is a diagram of the personal alarm device 60 and the magnetic field generator 81 of the proximity detection system of FIG. 1. The magnetic field generator 81 is contained within a housing 80 and includes an amplifier 84 connected to a ferrite core 90, inductor 86 and capacitor 88. In addition, the magnetic field generator 81 is connected to a power source 83 that provides the power to operate the magnetic field generator 81. The amplifier 84 is connected to and controlled by a controller 82. The ferrite core 90, inductor 86 and capacitor 88 generate a magnetic field 92 in response to an input voltage from the amplifier 84. The amplifier 84 is controlled by the controller 82 which controls the voltage and current outputs of the amplifier 84. The controller 82 is also connected to a receiver 96 and warning system 98. The receiver 96 is connected to an antenna 94 which receives an input signal 76 from a personal alarm device 60. The antenna 94 conveys the signal 76 to the receiver 96 which passes the signal 76 to the controller 82. Upon receiving the signal 76 from the personal alarm device 60, the controller 82 directs the warning system 98 to issue a warning. In one embodiment, the warning system 98 may issue an audio and/or visual warning. In another embodiment, the warning system 98 may be capable of terminating the operation of a vehicle to which the warning system 98 is mounted, for example, the truck 304 of FIG. 1. The magnetic field generator 80 may also be mounted in a location in which it is desirable to warn a worker carrying a personal alarm device 60 of their proximity to the location.
The personal alarm device 60 has x, y, and z axis magnetic field antennas 62 that sense the magnetic field 92 produced by the magnetic field generator 81. The sensed magnetic field signal 92 is passed through filters 66 and an amplifier 68 to a signal detector 64. The signal detector 64 then passes information about the detected signal to a controller 70. The controller 70 activates a transmitter 72 which transmits a corresponding response signal 76 to the magnetic field 92 through an RF (radio frequency) antenna 74. In one embodiment, the response signal 76 is an RF signal. The personal alarm device 60 is powered by power source 71. The personal alarm device 60 is carried by the worker 301 (FIG. 1) in order to provide the worker with a warning of their proximity to a magnetic field generator 81.
Proximity detection systems are beginning to be deployed in many types of mining operations around the world in an effort to avert mining accidents related to the use of machines and vehicles. As this technology advances, there is an increased need for higher performance from these systems.
The components of a PAD may include an antenna for detecting the marker field, a signal generator, visual and auditory alarms, and associated batteries, electronics, firmware, software, wiring, housing and mounting structure, and/or other components including those described in the Frederick patents.
Piezoelectric sounders have been used as part of the PADs to generate an audible alarm because such sounders use little power when producing a sufficiently loud sound, and because they are small in size. However, such piezoelectric sounders have a characteristic that causes a problem when used with a low frequency magnetic field system. These type sounders emit electromagnetic interference (EMI) in the low frequency spectrum which introduces noise into the sensing coils.
In work environments where hard hats are being used, it is effective to place the warning devices on the hard hat so that an alarm can be seen within the peripheral vision of the worker (i.e., in the line of sight) and/or so that the audible alarm is near their ear so that it can be heard even in noisy environments. See the '512 publication for a description of a hard hat positioned PAD. When used on a hard hat, the warning device portion of the PAD can be physically separated from the sensor portion by a sufficient distance to prevent the EMI from degrading proper operation. This is typically accomplished by positioning the sensor portion on the back of the hard hat and positioning the warning portion near the front of the hard hat, e.g., on the brim. If a hard had is not being used, then this separation must be accomplished by other means. Cables have been used which allow for the warning device portion to be in a shirt pocket, where it can be seen and heard, while the sensor portion is on a belt.
Also, placement of the device on the hard hat ensures that the device will always be present as part of the hard hat, a mandatory requirement in many industrial operations, and not left behind or lost. Workers who are busy with the many things required for their jobs do not like to have to keep up with safety devices. Mounting PAD components on the hard hat eliminates a nuisance for the worker and results in better acceptance and compliance. However, although many industrial operations require wearing a hard hat, many others do not. Therefore, another approach is required.
Multiple pockets on a vest have also been tried for holding various components of a PAD, with the piezoelectric sounder component (warning device portion) pocket being positioned a sufficient distance from the antenna component (sensor portion) pocket. However, acceptance of the PAD by the user will be improved if the sounder and antenna can be included in a single, integrated PAD unit. To use this approach, the piezoelectric sounder emitted EMI noise inducement problem must be solved.
The manner in which workers are given alerts or warnings is important. Alarms given to the worker should be implemented so as to ensure that they will not be missed or ignored but must also not be a nuisance to the person who is using them. There is a need for improvement of the available alarm devices, so that they effectively satisfy these two requirements as well as being practical to use.